Final answer:
A population demographic for people between 20 and 30 years old can be expressed with the inequality 20 <= x <= 30, where x is the age. Data on age demographics is crucial for planning social services for age-specific needs.
Step-by-step explanation:
The population demographic defined as someone 20 and older, but at most 30 years of age, can be expressed using inequalities as 20 ≤ x ≤ 30, where x represents an individual's age.
This indicates that the age x is greater than or equal to 20 and less than or equal to 30.
Regarding population demographics, the U.S. Census Bureau provides data and projections on population size, the increasing share of the elderly, differences in age distribution among countries, and the impacts of these changes on society.
These are important considerations as countries plan for future healthcare, economic support, and other social services to accommodate changing age dynamics.